In the GE-PON (Gigabit Ethernet (registered trademark) Passive Optical Network) achieving a communication speed of 1 gigabit/second through the public communication line network using an optical fiber, a light receiving element detects a light signal from a premises device, and a TIA (trans-impedance amplifier), that is, a preamplifier for amplifying the detection current output from this light receiving element is provided in a station side device.
For example, Japanese Patent Laying-Open No. 63-151205 (Patent Document 1) discloses the following configuration as a conventional preamplifier, in which a light receiving circuit outputs, through a preamplifier, the output current of an avalanche photodiode as an output voltage that varies depending on the light input and controls this output voltage by an AGC (Automatic Gain Control) circuit. The light receiving circuit includes a saturation voltage detection circuit for detecting saturation of the output voltage of the preamplifier, and a diversion circuit for diverting the output current of the avalanche photodiode in response to the output of the saturation voltage detection circuit.
Furthermore, Japanese Patent Laying-Open No. 09-008563 (Patent Document 2) discloses the configuration having a light receiving preamplifier for amplifying a current signal from a light receiving element. The light receiving preamplifier includes a feedback amplifier circuit configured to vary the gain phase characteristics by the first control signal in accordance with the magnitude of the current signal; and a large input control circuit configured to compare the output of the feedback amplifier circuit with the reference voltage to output the first control signal to the feedback amplifier circuit. The feedback amplifier circuit consists of an amplifier for amplifying the current signal, a buffer circuit for buffering the output of the amplifier, the first and second feedback resistances for switching the gain of the amplifier, a phase compensation capacitor for performing phase compensation of the amplifier, and the first and second switch elements for performing the switching operation for the gain and phase compensation.
Furthermore, Japanese Patent Laying-Open No. 2006-101223 (Patent Document 3) discloses the configuration including an inverting amplifier circuit to which a burst signal is input; the first feedback circuit disposed between the input node and the output node of the inverting amplifier circuit; the second feedback circuit disposed in parallel with the first feedback circuit; a burst section determination unit for determining the duration period of the burst signal, based on the output of the inverting amplifier circuit, and outputting the first signal indicative of an off period of the burst signal; and a gain switching signal generation unit for determining the amplitude of the burst signal, based on the output of the inverting amplifier circuit, and outputting the second signal indicating that the amplitude has exceeded a predetermined threshold value. The second feedback circuit includes a phase compensation capacitor and a switch that is controlled to be opened and closed based on the first and second signals, in which the gain is controlled by opening and closing the switch.    Patent Document 1: Japanese Patent Laying-Open No. 63-151205    Patent Document 2: Japanese Patent Laying-Open No. 09-008563    Patent Document 3: Japanese Patent Laying-Open No. 2006-101223